Displaying a logarithmic value on a linear plot

[sdp54321]

Hi all,

I am having a mental block and hard time wrapping my head around this issue and how to do it. Let me explain.

I am using LabView to drive a Built-in-Self-Test (BIST) on our product. The device has a front panel touchscreen with serial control. 

If you look at the attachment you will see a graphic (made in LabView) which will be displayed on the touchscreen.

The device BIST will feed me the bit-error-rate value (BER) such as 1e-5 errors. 

I want to drop a dot on this graph for this error rate at a certain X value on the graph

My Y range is as follows: 1e-1 = 10 and 1e-9 = 300

Therefore, I have 290 pixels between the top and bottom of my scale.

290/8 = 36.25 pixels for each interval.

1e-1 = 10

1e-2 = 46.25

1e-3 = 82.50

etc...

I need to mathematically convert this number to show logarithmically on an x-y scale.

While writing this, I layed out 10 points from 1e-2 to 1e-1 (see Scsreenshot331).. I'm seeing the pattern but can't get the math right.

Plus I need to expand it down to 1e-9.

Thanks,

Peter

[GerdW]

Hi Peter,

Pixel is log(y) * 36.25 + offset...

[natasftw]

Why don't you just go to the properties dialog?  Go to Scales and check the box for Log.

THat makes your x-scale logarithmic.  No need for fancy math.

[sdp54321]

natasftw, you didn't understand.  The device I need to write to is a simple x-y screen. I am not graphing in Windows and the LabView environment.

GerdW... That is exactly where I was going... close... but that doesn't work either.

I did figure it out though.

What complicated it for me was that all my Y-paramenters are <1. Log of anything less than 1 is a negative number.

It turns out that the formula is as follows.

pixel = (abs(log(y) -1)) * 36.25 +10

[GerdW · Accepted solution]

Hi sdp,

pixel = (abs(log(y) -1)) * 36.25 +10

pixel = log(y)*(-36.25) - 26.25 (for 1e-9<=y<=1e-1)

One function less, one addition less…

[sdp54321]

Hi Gerd,

Interesting.... I never think about simplifying.

My code is very clean and readable, but reducing unnecessary steps is something I fail to implement.

I guess if my program had speed critical constraints , I would probably need to be more diligent with that.

Peter